Closed-captioning (CC) is a video-related service that was developed for the hearing-impaired. When CC is enabled, video and text representing an audio portion of the video are displayed as the video is played. The text may represent, for example, spoken dialog or sound effects of the video, thereby helping a viewer to comprehend what is being presented in the video. CC may also be disabled such that the video may be displayed without such text as the video is played. In some instances, CC may be enabled or disabled while a video is being played.
CC captioning text may be generated in a variety of manners. For example, an individual may listen to an audio portion of video and manually type out corresponding text. As another example, a computer-based automatic speech-recognition system may convert spoken dialog from video to text.
Once generated, CC text may be encoded and stored in the form of CC data. CC data may be embedded in or otherwise associated with the corresponding video. For example, for video that is broadcast in an analog format according to the National Television Systems Committee (NTSC) standard, the CC data may be stored in line twenty-one of the vertical blanking interval of the video, which is a portion of the television picture that resides just above a visible portion. Storing CC data in this manner involves demarcating the CC data into multiple portions (referred to herein as “CC blocks”) such that each CC block may be embedded in a correlating frame of the video based on a common processing time. In one example, a CC block represents two characters of text. However a CC block may represent more or less characters.
For video that is broadcast in a digital format according to the Advanced Television Systems Committee (ATSC) standard, the CC data may be stored as a data stream that is associated with the video. Similar to the example above, the CC data may be demarcated into multiple CC blocks, with each CC block having a correlating frame of the video based on a common processing time. Such correlations may be defined in the data stream. Notably, other techniques for storing video and/or associated CC data are also possible.
A receiver (e.g., a television) may receive and display video. If the video is encoded, the receiver may receive, decode, and then display each frame of the video. Further, the receiver may receive and display CC data. In particular, the receiver may receive, decode, and display each CC block of CC data. Typically, the receiver displays each frame and a respective correlating CC block as described above at or about the same time.